1. Field of the Invention
This invention relates to a changing device for changing the plastic material to be supplied to a horizontal injecting unit comprising a plasticizing cylinder which is mounted at its rear end in a carrier block, which changing device comprises a guide bar, which extends transversely to the injection axis of the injecting unit and has a through bore, which together with a supply passage of said carrier block constitutes a passage leading into the plasticizing cylinder, said changing device also comprises a traversing plate, which is movable along the guide bar and is formed with port bores, which are adapted to be closed by respective gates and to which respective feed hoses are adapted to be connected, which are adapted to supply the plasticizing cylinder with different plastic materials from respective supply bins, also comprises a traversing drive for moving the traversing plate in steps to any of a plurality of feed positions, in which respective port bores of the traversing plate register with the through bore of the guide bar.
2. Description of the Prior Art
A known changing device of that kind is disclosed in U.S. Pat. No. 4,731,005 and comprises an axially fixed ball screw, which is motor-driven and drives the traversing plate. Because the traversing plate which is operated by said ball screw can be continuously displaced, expensive electronic means (displacement measuring devices, limit switches) are required to ensure that the selected port bore of the traversing plate will be properly in register with the through bore in the carrier block when the associated gate is opened.